Synthetic hydrocarbons have been used as lubricant components for automotive, aviation, and industrial applications. In the automotive industry, lubricant oils include engine oils, brake fluids, and lubricating greases. Engine oils for an automobile include 2-stroke oils, 4-stroke oils, and gear oils. In the aviation industry, lubricant oils include turbine oils, piston engine oils, hydraulic fluids, and lubricating greases. In industrial applications, lubricant oils are used as gas-turbine oils, gear oils, bearing and circulation oils, compressor oils, hydraulic oils, metal-working fluids, heat-transfer and insulation oils, and lubricating greases.
Poly-α-olefins (PAOs; polyalphaolefins) are synthetic hydrocarbons which have been used as lubricant base oils. PAOs have good flow properties at low temperatures, relatively high thermal and oxidative stability, low evaporation losses at high temperatures, higher viscosity index, good friction behavior, good hydrolytical stability, and good erosion resistance. PAOs are not toxic and are miscible with mineral oils and esters. Consequently, PAOs are suited for use in engine oils, compressor oils, hydraulic oils, gear oils, and greases. However, PAOs that have been characterized to date, have limited oxidative stability, limited biodegradability and limited additive miscibility. Therefore, it may not be suitable for use as high-performance gear oils and fast biodegradable oils. Structurally, PAOs often include tertiary hydrogen which is prone to oxidation. Therefore, it would be desirable to minimize the presence of tertiary hydrogen so as to improve oxidation resistance of synthetic hydrocarbons.
Currently, PAOs are synthesized by a two-step reaction sequence from linear α-olefins, which are derived from ethylene. The first step is the synthesis of a mixture of oligomers, which are polymers of relatively low molecular weight. This first step is catalyzed using a boron trifluoride catalyst in conjunction with a protic catalyst such as water, alcohol, or a weak carboxylic acid. However, it has been observed that boron trifluoride catalysis causes excess skeletal branching during the oligomerization process. An increase in the amount of skeletal branching directly correlates with an increase in the number of tertiary hydrogens in the molecule, which are prone to oxidation, and therefore exhibit poor stability when used in lubricants. The second step in the manufacturing process entails hydrogenation of the unsaturated oligomer.
Due to the increasing demand for product performance, there is a need for a relatively more stable PAO and a lubricant made therefrom. A PAO made in a process in which no substantially additional tertiary hydrogens are introduced during oligomerization, would be less prone to oxidation, and would possess greater stability than the branched PAOs currently known in the art. This type of PAO is hereafter referred to as a non-isomerized oligomer.